This invention relates generally to a print wheel printer and more particularly to a printer wherein printing is performed by selection of corresponding symbols or characters on rotated print wheels by utilizing a plurality of independent and operatively selective pawls.
A print wheel printer generally comprises a plurality of print wheels which are secured to corresponding ratchet wheels, a plurality of selective pawls which stop the rotation of print wheels at selective rotational positions by engaging corresponding notches of the ratchet wheels, a plurality of electromagnetic mechanisms which rotate selected pawls to bring them into selective engagement positions with corresponding ratchet wheels, a reset lever for collectively returning all of the pawls from a print wheel engaging position to a print wheel disengaging position and a reset cam changing the positional relationship of the reset lever relative to the pawls.
As it is disclosed in Japan Laid Open Patent 144521/75, the positioning members for spatially positioning the print wheels along the print wheel shaft and the separate construction of the selective pawls on the main housing frame of the printer result in many different steps necessary for assembling together these many printer parts. Further, since positioning of these parts are determined indirectly relative to the main housing frame of the printer due to their support relative to the housing, as well as relative positional aberrations due to the lack of precision of the manufactured printer parts and the required assembly of many different parts involved, render it always necessary to perform fine adjustments after the assembly of the printer parts.
Also, since the reset lever in these printers is fixed on a trigger unit casing via a support shaft, it is necessary to disengage the trigger unit from the main housing frame each time when the reset lever is to be removed and replaced onto to trigger unit casing.
It is an object of the present invention to provide a print wheel printer wherein assembly of a plurality of parts which perform functions in connection with the operation of the print wheels is performed easily and with high precision.
It is another object of this invention to provide a simpler and more precise positioning of the print wheels of a print wheel printer.
It is still another objective of this invention to render it possible to remove and reposition a reset lever while the trigger unit casing remains secured to the main housing frame of the print wheel printer.